Question

如果我使用此查询：

SELECT clinic.id
FROM clinic 
JOIN dentist ON dentist.id = clinic.dentist_id 
JOIN user ON user.id = dentist.user_id 
WHERE user.status = 'Active'
AND clinic.status = 'Approved'
AND user.role_id = 2
GROUP BY clinic.id;

所以它给了我所有的行像

错误如果我要获得结果的总数，那么我应用查询：

SELECT count(clinic.id) AS cnt
FROM clinic 
JOIN dentist ON dentist.id = clinic.dentist_id 
JOIN user ON user.id = dentist.user_id 
WHERE user.status = 'Active'
AND clinic.status = 'Approved'
AND user.role_id = 2
GROUP BY clinic.id;

我刚刚将count（）应用于id，然后返回

它不返回7，我想要结果为7。请有人指导。

Answer 1

请勿使用GROUP BY 或尝试此

SELECT clinicID,SUM(case when clinic !=null then 1 ELSE NULL END).id AS cnt
FROM clinic 
JOIN dentist ON dentist.id = clinic.dentist_id 
JOIN user ON user.id = dentist.user_id 
WHERE user.status = 'Active'
AND clinic.status = 'Approved'
AND user.role_id = 2
GROUP BY clinic.id;

Answer 2

我可以看到两个选择。由于您正在进行分组，因此您将获得每组的计数，这是预期的行为。要获得总计数，您需要删除group by并执行此操作：

SELECT count(distinct clinic.id)
FROM clinic 
  JOIN dentist ON dentist.id = clinic.dentist_id 
  JOIN user ON user.id = dentist.user_id 
WHERE user.status = 'Active' 
 AND clinic.status = 'Approved' 
 AND user.role_id = 2

或者只是在新查询中使用您的第一个查询作为子查询，如下所示：

select count(*) from (
  SELECT clinic.id
  FROM clinic 
    JOIN dentist ON dentist.id = clinic.dentist_id 
    JOIN user ON user.id = dentist.user_id 
  WHERE user.status = 'Active' 
    AND clinic.status = 'Approved' 
    AND user.role_id = 2  
  GROUP BY clinic.id) q

Answer 3

SELECT count(clinic.id) AS cnt
FROM 
clinic 
JOIN dentist ON dentist.id = clinic.dentist_id 
JOIN user ON user.id = dentist.user_id 
WHERE user.status = 'Active' AND clinic.status = 'Approved' AND user.role_id = 2

删除GROUP BY子句。

mysql不能使用join和where子句

3 个答案: